Two-photon absorption (2PA) has been used for a number of scientific and technological applications, exploiting the fact that the 2PA probability is directly proportional to the square of the incident light intensity (while one-photon absorption bears a linear relation to the incident light intensity). This intrinsic property of 2PA leads to 3D spatial localization, important in fields such as optical data storage, fluorescence microscopy, and 3D microfabrication. The spatial confinement that 2PA enables has been used to induce photochemical and photophysical events in increasingly smaller volumes and allowed nonlinear, 2PA-based, technologies to reach sub-diffraction limit resolutions. The primary focus of this dissertation is the development of novel, efficient 2PA, fluorene-based molecules to be used either as photoacid generators (PAGs) or fluorophores. A second aim is to develop more effective methods of synthesizing these compounds. As a third and final objective, the new molecules were used to develop a write-once-read many (WORM) optical data storage system, and stimulated emission depletion probes for bioimaging. In Chapter I, the microwave-assisted synthesis of triarylsulfonium salt photoacid generators (PAGs) from their diphenyliodonium counterparts is reported. The microwave-assisted synthesis of these novel sulfonium salts afforded reaction times 90 to 420 times faster than conventional thermal conditions, with photoacid quantum yields of new sulfonium PAGs ranging from 0.01 to 0.4. These PAGs were used to develop a fluorescence readout-based, nonlinear three-dimensional (3D) optical data storage system (Chapter II). In this system, writing was achieved by acid generation upon two-photon absorption (2PA) of a PAG (at 710 or 730 nm). Readout was then performed by interrogating two-photon absorbing dyes, after protonation, at 860 nm. Two-photon recording and readout of voxels was demonstrated in five and eight consecutive, crosstalk-free layers within a polymer matrix, generating a data storage capacity of up to 1.8 x 1013 bits/cm3. The possibility of using these PAGs in microfabrication is described in Chapter III, where two-photon induced cationic ring-opening polymerization (CROP) crosslinking of an SU8 resin is employed to produce free-standing microstructures. Chapter IV describes the investigation of one- and two-photon stimulated emission transitions by the fluorescence quenching of a sulfonyl-containing fluorene compound in solution at room temperate using a picosecond pump-probe technique. The nature of stimulated transitions under various fluorescence excitation and quenching conditions were analyzed theoretically, and good agreement with experimental data was demonstrated. Two-photon stimulated transitions S1 to S0 were shown at 1064 nm. The two-photon stimulated emission cross section of the sulfonyl fluorophore was estimated as aproximately 240 - 280 GM, making this compound a good candidate for use in two-photon stimulated emission depletion (STED) microscopy.

This Thesis describes the systematic theoretical study aimed at prediction of the essential properties for the functional organic molecules that belong to diarylethene (DA) family of compounds. Diarylethenes present the distinct ability to change color under the influence of light, known as photochromism. This change is due to ultrafast chemical transition from open to closed ring isomers (photocyclization). It can be used for optical data storage, photoswitching, and other photonic applications. In this work we apply Density Functional Theory methods to predict 6 of the related properties: (i) molecular geometry; (ii) resonant wavelength; (iii) thermal stability; (iv) fatigue resistance; (v) quantum yield and (vi) nanoscale organization of the material. In order to study sensitivity at diode laser wavelengths, we optimized geometry and calculated vertical absorption spectra for a benchmark set of 28 diarylethenes. Bond length alternation (BLA) parameters and maximum absorption wavelengths (λmax) are compared to the data presently available from X-ray diffraction and spectroscopy experiments. We conclude that TD-M05/6-31G*/PCM//M05-2X/6-31G*/PCM level of theory gives the best agreement for both the parameters. For our predictions the root mean square deviation (RMSD) are below 0.014 Å for the BLAs and 25 nm for λmax. The polarization functions in the basis set and solvent effects are both important for this agreement. Next we consider thermal stability. Our results suggest that UB3LYP and UM05-2X functionals predict the activation barrier for the cycloreversion reaction within 3-4 kcal/mol from experimental value for a set of 7 photochromic compounds. We also study thermal fatigue, defined as the rate of undesirable photochemical side reactions. In order to predict the kinetics of photochemical fatigue, we investigate the mechanism of by-product formation. It has been established experimentally that the by-product is formed from the closed isomer; however the mechanism was not known. We found that the thermal by-product pathway involves the bicyclohexane (BCH) ring formation as a stable intermediate, while the photochemical by-product formation pathway may involve the methylcyclopentene diradical (MCPD) intermediate. At UM05-2X/6-31G* level, the calculated barrier between the closed form and the BCH intermediate is 51.2 kcal/mol and the barrier between the BCH intermediate and the by-product 16.2 kcal/mol. Next we investigate two theoretical approaches to the prediction of quantum yield (QY) for a set of 14 diarylethene derivatives at the validated M05-2X/6-31G* theory level. These include population of ground-state conformers and location of the pericycylic minimum on the potential energy surface 2-A state. Finally, we investigate the possibility of nanoscale organization of the photochromic material based on DNA template, as an alternative to the amorphous polymer matrix. Here we demonstrate that Molecular Dynamic methods are capable to describe the intercalation of π-conjugated systems between DNA base pairs and accurately reproduced the available photophysical properties of these nanocomposites. In summary, our results are in good agreement with the experimental data for the benchmark set of molecules we conclude that Density Functional Theory methods could be successfully used as an important component of material design strategy in prediction of accurate molecular geometry, absorption spectra, thermal stability of isomers, fatigue resistance, quantum yield of photocyclization and photophysical properties of nanocomposites.

No description available.

Thesis: M.S., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 1980 / Includes bibliographical references. / by Peter Maynard Osterberg. / M.S. / M.S. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science

No description available.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographcial references. / by Helen Louise Graham. / M.S.

Object recognition--"What is in this image?"--is one of the basic problems of computer vision. Most work in this area has been on finding basic-level object categories such as plant, car, and bird, but recently there has been an increasing amount of work in fine-grained visual categorization, in which the task is to recognize subcategories of a basic-level category, such as blue jay and bluebird. Experimental psychology has found that while basic-level categories are distinguished by the presence or absence of parts (a bird has a beak but car does not), subcategories are more often distinguished by the characteristics of their parts (a starling has a narrow, yellow beak while a cardinal has a wide, red beak). In this thesis we tackle fine-grained visual categorization, guided by this observation. We develop alignment procedures that let us compare corresponding parts, build classifiers tailored to finding the interclass differences at each part, and then combine the per-part classifiers to build subcategory classifiers. Using this approach, we outperform previous work in several fine-grained categorization settings: bird species identification, face recognition, and face attribute classification. In addition, the construction of subcategory classifiers from part classifiers allows us to automatically determine which parts are most relevant when distinguishing between any two subcategories. We can use this to generate illustrations of the differences between subcategories. To demonstrate this, we have built a digital field guide to North American birds which includes automatically generated images highlighting the key differences between visually similar species. This guide, "Birdsnap," also identifies bird species in users' uploaded photos using our subcategory classifiers. We have released Birdsnap as a web site and iPhone application.

Thesis submitted in fulfilment of the requirements for the degree Doctor of Technology: Electrical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2014 / Three-dimensional (3D) artefact detection can provide the conception of vision and real time interaction of electronic products with devices. The orientation and interaction of electrical systems with objects can be obtained. The introduction of electronic vision detection can be used in multiple applications, from industry, in robotics and also to give orientation to humans to their immediate surroundings. An article covering holograms states that these images can provide information about an object that can be examined from different angles. The limitations of a hologram are that there must be absolute immobilization of the object and the image system. Humans are capable of stereoscopic vision where two images are fused together to provide a 3D view of an object. In this research, two digital images are used to determine the artefact position in space. The application of a camera is utilized and the 3D coordinates of the artefact are determined. To obtain the 3D position, the principles of the pinhole camera, a single lens as well as two image visualizations are applied. This study explains the method used to determine the artefact position in space. To obtain the 3D position of an artefact with a single image was derived. The mathematical formulae are derived to determine the 3D position of an artefact in space and these formulae are applied in the pinhole camera setup to determine the 3D position. The application is also applied in the X-ray spectrum, where the length of structures can be obtained using the mathematical principles derived. The XYZ coordinates are determined, a computer simulation as well as the experimental results are explained. With this 3D detection method, devices can be connected to a computer to have real time image updates and interaction of objects in an XYZ coordinate system. Keywords: 3D point, xyz-coordinates, lens, hologram

No description available.

Le stockage de données par holographie suscite un intérêt renouvelé. Il semble bien placé pour conduire à une nouvelle génération de mémoires optiques aux capacités et débits de lecture bien supérieurs à ceux des disques optiques actuels basés sur l’enregistrement dit surfacique. Dans ce travail de thèse, nous proposons une nouvelle architecture de stockage optique de données qui s’inspire du principe de la photographie interférentielle de Lippmann. Les informations y sont inscrites dans le volume du matériau d’enregistrement sous la forme de pages de données par multiplexage en longueur d’onde en exploitant la sélectivité de Bragg. Cette technique, bien que très voisine de l’holographie, n’avait jamais été envisagée pour le stockage à hautes capacités. L’objectif de la thèse a été d’analyser cette nouvelle architecture afin de déterminer les conditions pouvant conduire à de très hautes capacités. Cette analyse s’est appuyée sur un outil de simulation numérique des processus de diffraction en jeu dans cette mémoire interférentielle. Elle nous a permis de définir deux conditions sous lesquelles ces hautes capacités sont atteignables. En respectant ces conditions, nous avons conçu un démonstrateur de mémoire dit de « Lippmann » et avons ainsi démontré expérimentalement que la capacité est bien proportionnelle à l’épaisseur du matériau d’enregistrement. Avec une telle architecture, des capacités de l’ordre du Téraoctet sont attendues pour des disques de 12 cm de diamètre. / Nowadays, the holographic data storage presents a renewed interest. It seems well placed to lead a new generation of optical storage capacity and playback speeds much higher than current optical discs based on the recording onto a surface. In this thesis, we propose a new architecture for optical data storage that is based on the principle of Lippmann photography interferential. Information are included in the volume of the recording material in the form of pages of data multiplexing in wavelength by exploiting the Bragg selectivity. This technique, although very similar to holography, had never been considered for high storage capacities. The aim of the thesis was to analyze this new architecture to determine the conditions that can lead to very high capacities. This analysis was based on a numerical simulation tool of diffraction process involved in this memory interferential. It allowed us to define two conditions under which these high capacities are achievable. In accordance with these conditions, we developed a demonstrator called "Lippmann’s memory" and have thus demonstrated experimentally that the capacity is proportional to the thickness of the recording material. With such an architecture, Terabyte disks of 12 cm in diameter are expected.